1. Field of the Invention
The present invention generally relates to a fuel injection control apparatus for internal combustion engines, and, more particularly, to a fuel injection apparatus equipped with a pressure regulator in or in the vicinity of a fuel tank.
2. Description of the Related Art
Generally, an internal combustion engine equipped with an electronic fuel injection control apparatus includes a pressure regulator in or in the vicinity of an engine room, which utilizes the negative intake pressure as a control parameter for the fuel injection. This pressure regulator returns part of the fuel to the fuel tank through a return pipe when the pressure of fuel supplied from a fuel pump to a fuel injection valve rises higher than the pressure of an intake pipe, whereby the differential pressure between the intake negative pressure and the fuel pressure is maintained at a constant value.(as disclosed in the Japanese Unexamined Patent Publication No. 64-32066, etc.)
However, according to the above-described pressure regulator, the return pipe for returning part of the fuel to the fuel tank should be extended from the engine room generally provided in the front position of a vehicle to the fuel tank generally provided in the rear position of the vehicle. Therefore, the mounting efficiency of the pressure regulator is not sufficient.
To simplify the return pipe, a system wherein the pressure regulator is provided in or in the vicinity of the fuel tank is conceived. An object of such system is to eliminate an intake negative pressure introduction pipe, which extends from the pressure regulator to an intake manifold, such as a surge tank, for suppressing the pulsation in the intake manifold, by maintaining the differential pressure between the pressure around the pressure regulator and the fuel pressure instead of maintaining the differential pressure between the intake pressure and the fuel pressure at a constant value.
A problem with the above system is that, as the pressure of the fuel to be supplied to an injection valve is maintained constant in proportion to the pressure in or in the vicinity of the fuel tank, when the intake pressure varies, the fuel injection quantity varies, despite the open operation time of the injection valve remain unchanged.